On Sat, Sep 27, 2014 at 08:07:25PM +0200, Oleg Nesterov wrote: > On 09/26, Sylvain 'ythier' Hitier wrote: > > > > retval = sched_fork(clone_flags, p); > > if (retval) > > // // mustn't perf_event_free_task() > > goto bad_fork_cleanup_policy; > > Agreed, this is wrong. Good catch. > > but, unless I missed something,
Ah, indeed. It was meant to be a no-op there, but its before we do that memset, so its still the inherited values, and we don't want to clean those up I think. > > retval = perf_event_init_task(p); > > if (retval) > > // // mustn't perf_event_free_task() > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > > this is not right and thus the patch is not right too. Agreed > Suppose that perf_event_init_task() -> perf_event_init_context(ctxn => 0) > succeeds and then perf_event_init_context(ctxn => 1) fails, we need > perf_event_free_task() to cleanup ->perf_event_ctxp[0]. > > So if perf_event_init_task() fails, we still need "goto > bad_fork_cleanup_perf". > > No? Yep > Or, probably better, we need to change perf_event_init_context() to call > perf_event_free_task() on failure. > > Or. We can simply move memset(child->perf_event_ctxp, 0, ...) from > perf_event_init_context() up. This reminds that we really need to cleanup > copy_process(), in particular I think it asks for the new copy_xxx() helper > which should do misc simple initializations which can't fail. > > What do you think? I prefer the former, as the latter scatters the perf specific bits over more places. Something like so then? --- Subject: perf: Fix perf bug in fork() Oleg noticed that a cleanup by Sylvain actually uncovered a bug; by calling perf_event_free_task() when failing sched_fork() we will not yet have done the memset() on ->perf_event_ctxp[] and will therefore try and 'free' the inherited contexts, which are still in use by the parent process. This is bad.. Suggested-by: Oleg Nesterov <[email protected]> Reported-by: Oleg Nesterov <[email protected]> Reported-by: Sylvain 'ythier' Hitier <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> --- diff --git a/kernel/events/core.c b/kernel/events/core.c index a232b40..4a0dbb2 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -8078,8 +8078,10 @@ int perf_event_init_task(struct task_struct *child) for_each_task_context_nr(ctxn) { ret = perf_event_init_context(child, ctxn); - if (ret) + if (ret) { + perf_event_free_task(child); return ret; + } } return 0; diff --git a/kernel/fork.c b/kernel/fork.c index ad64248..b6cc3f2 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1367,7 +1367,7 @@ static struct task_struct *copy_process(unsigned long clone_flags, goto bad_fork_cleanup_policy; retval = audit_alloc(p); if (retval) - goto bad_fork_cleanup_policy; + goto bad_fork_cleanup_perf; /* copy all the process information */ shm_init_task(p); retval = copy_semundo(clone_flags, p); @@ -1573,8 +1573,9 @@ bad_fork_cleanup_semundo: exit_sem(p); bad_fork_cleanup_audit: audit_free(p); -bad_fork_cleanup_policy: +bad_fork_cleanup_perf: perf_event_free_task(p); +bad_fork_cleanup_policy: #ifdef CONFIG_NUMA mpol_put(p->mempolicy); bad_fork_cleanup_threadgroup_lock: -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
